Re: [LAD] [ot] rme fireface: weird balanced output measurements

Something I didn't consider in my first generation design since I was still learning myself, which although it had an output impedance at the TLO84 pin of under an ohm, then used 300 ohm per leg build outs. The next generation card, the main design change was to change that 300 ohm to 30 ohms. This then worked much better out in the newsroom, but was even more susceptible to the emp spikes the longer runs picked up. Since the card had to fit the cage, it never did grow the schotkey power diodes to the supply rails that would have absorbed those spikes, no room left on the the card for diodes that at the time (1984-85) were about 1/2" long & 1/4" in diameter. It would have taken 12 of them to protect the inputs as well as the outputs. These cards all had their own rail regulators (78-7915's) for +-15 volts as the cage supply was about 22 volts +-, filtered some but not regulated, good for about 10 amps a rail. 22 cards with 44 pin edge connectors in one 3 space high rack, it did have noticeable but tolerable heat output. The only place with enough farads available to dump the emp was the main rails, and a quick test of that idea using a bench supply showed that wasn't a cure as the output stage of the TLO84 was still destroyed when the output was pulled above or below the cards internal +-15 volts by about 2 volts, long before the schotkeys to the +-22 volt rail would turn on.

So now the problem is levels, digital doesn't come with a knob. The std, if there even is one, is ignored, which explains the commercials that are 20db louder than the program, nobody cares and we catch hell from the listeners.